Described in U.S. Pat. No. 4,663,917 is a packaging machine. The packaging machine receives tubular bag material to the interior of which product is delivered. The tubular bag material is formed from a web (strip) that via a former is transformed into the tubular configuration. The longitudinally extending edge portions of the web are joined so as to form a longitudinal seal. Product is delivered to the interior of the tubular bag material, with the packaging machine then transversely sealing are of cutting the tubular bag material, at longitudinally spaced locations, to form bags.
If the longitudinal and/or transverse seals are not properly formed, the product can degrade. Various means have been proposed for checking the integrity of the seals. As an example, seal testing devices are described in U.S. Pat. Nos. 6,568,247, 6,202,476 and 6,041,646.
Previous methods of detecting improperly formed seals have a number of disadvantages including not successful detecting faulty seals, and being unduly complex and unreliable.